Student activist Panupong Jadnok was detained on Monday while he was protesting in Rayong outside a market being visited by Prime Minister Prayut Chan-o-cha.
Mr Panupong, also known as Mike Rayong, was waving a banner opposing a land reclamation scheme at Ban Phe municipality market when police showed up with an arrest warrant.
Gen Prayut and his cabinet ministers were visiting the market ahead of Tuesday's mobile cabinet meeting in Rayong.
The arrest was made with a warrant issued by Thanyaburi Court over Mr Panupong's role in the Aug 10 political gathering at Thammasat University's Rangsit campus in Pathum Thani.
Mr Panupong had been bailed after being arrested on Aug 8 along with lawyer Arnon Nampa for his role in the July 18 anti-government protest at Democracy Monument.
He said Monday's protest had nothing to do with politics and he only showed up to ask questions about the reclamation project in Rayong. However, he acknowledged the warrant and was whisked away in a van to Ban Phe police station.
Meanwhile, Pol Maj Gen Somprasong Yenthuam, deputy commissioner of the Metropolitan Police Bureau, said officers had found no evidence to press charges against protest leaders involved in the Aug 16 rally at the Democracy Monument.
He said the offences committed were minor and the most police might do was invite the offenders in for talks.
As for the Aug 23 rally in front of City Hall, he said police were examining whether any protest leaders charged in connection with the previous gathering had violated their bail conditions by taking part.
Pol Maj Gen Somprasong also confirmed that a memo ordering the dispatch of an electronic monitoring device to the site of Sunday's rally was genuine and part of security precautions at protest venues.
He insisted that the equipment was not there to disrupt mobile phone signals and thus infringe on protesters' rights and would be used only when a suspicious-looking subject was detected.
Provincial Police Region 3 and Provincial Police Region 7 were on Monday said to have ordered crowd-control units to report for training ahead of a mass rally planned by anti-government protesters in Bangkok on Sept 19.
Meanwhile, Sonthiya Sawatdee, a former member of the ruling Palang Pracharath Party, on Monday lodged a complaint with the Constitutional Court, asking it to rule whether the political rallies aimed to overthrow the system.
He said the petition was prompted by the protesters' demand for a House dissolution, the setting up of a charter-writing body and an end to alleged harassment of political activists.
He said the MPs had been elected through a legitimate poll and the 2007 charter adopted following a public referendum.